Asymptomatic and symptomatic oropharyngeal disorders can lead to an inability to swallow or difficulty in swallowing. These disorders may be caused, for example, by stroke. neurodegenerative diseases, brain tumors or respiratory disorders.
Swallowing is a complicated action whereby food is moved from the mouth through the pharynx and esophagus to the stomach. The act of swallowing may be initiated voluntarily or reflexively but is always completed reflexively.
The act of swallowing occurs in three stages and requires the integrated action of the respiratory center and motor functions of multiple cranial nerves, and the coordination of the autonomic system within the esophagus. In the first stage, food or some other substance is placed on the surface of the tongue. The tip of the tongue is placed against the hard palate. Elevation of the larynx and backward movement of the tongue forces the food through the isthmus of the fauces in the pharynx. In the second stage, the food passes through the pharynx. This involves constriction of the walls of the pharynx, backward bending of the epiglottis, and an upward and forward movement of the larynx and trachea. Food is kept from entering the nasal cavity by elevation of the soft palate and from entering the larynx by closure of the glottis and backward inclination of the epiglottis. During this stage, respiratory movements are inhibited by reflex. In the third stage, food moves down the esophagus and into the stomach. This movement is accomplished by momentum from the second stage, peristaltic contractions, and gravity.
Although the main function of swallowing is the propulsion of food from the mouth into the stomach, swallowing also serves as a protective reflex for the upper respiratory tract by removing particles trapped in the nasopharynx and oropharynx, returning materials to the stomach that are refluxed into the pharynx, or removing particles propelled from the upper respiratory tract into the pharynx. Therefore, the absence of adequate swallowing reflex greatly increases the chance of pulmonary aspiration.
In the past, patients suffering from oropharyngeal disorders have undergone dietary changes or thermal stimulation treatment to regain adequate swallowing reflexes. Thermal stimulation involves immersing a mirror or probe in ice or another cold substance. The tonsillar fossa is stimulated with the mirror or probe, and the patient closes his mouth and attempts to swallow. While these traditional methods are usually effective for treating oropharyngeal disorders, in some patients these methods require that the patient endure weeks or months of therapy. It is also difficult to distinguish patients who require such treatments from patients who recover spontaneously. Thus, it is desirable to have a simple, non-invasive method and device for treating oropharyngeal disorders and artificially promoting swallowing which is effective within a relatively short treatment period.
Electrical stimulation has been used as a method for alleviating pain and stimulating nerves, as well as a means for treating disorders of the spinal cord or peripheral nervous system. Electrical stimulation has further been used to facilitate muscle reeducation and with other physical therapy treatments. In the past, electrical stimulation was not recommended for use in the neck because of concerns that the patient would develop spasms of the laryngeal muscles, resulting in closure of the airway or difficulty in breathing, and/or because of concerns that the introduction of electrical current into the neck near the carotid body would cause cardiac arrhythmia.
More recently, electrical stimulation has been used to stimulate the recurrent laryngeal nerve to stimulate the laryngeal muscles to control the opening of the vocal cords to overcome vocal cord paralysis, to assist with the assessment of vocal cord function, to aid with intubation, and other related uses. Generally, there have been no adverse reactions to such treatment techniques. However, electrical stimulation has not been used in the treatment of oropharyngeal disorders to promote the swallowing reflex, which involves the integrated action of the respiratory center and motor functions of multiple cranial nerves.